1. Field of the Invention
The present invention relates to well bore drilling techniques, and more particularly to techniques for cooling the drilling fluids in response to the well bore temperatures.
2. Description of the Prior Art
In the course of drilling a well by rotary methods drilling mud is quite frequently circulated through the interior of a hollow drill pipe, the drilling mud being returned at the drill bit through the annular aperture between the drill pipe and the well bore to be collected at the surface in a container or a mud pit. Heretofore direct evaporative cooling of the drilling mud has been employed as the prime means of cooling the drill tip. As the bore depths increased in the recent past and as more and more drilling has been recently directed into geothermal areas the cooling demands on the drilling fluid or mud have significantly increased. Evaporative cooling, while possible in normal applications, thus becomes less and less acceptable with increasing well bore depths, particularly where large flow rates are entailed and large amounts of chips and drilling debris are brought up to the surface. Furthermore, evaporative cooling is fixed by the temperature differential above ambient temperature and in instances where deep well bores are drilled there is often insufficient lead response to accommodate the length of time that it takes for the drilling mud to return to the surface.